The purpose of this study is to investigate the process of unionization among practicing physicians. First, the Illinois Physicians' Union will be studied as an emergent formal organization. To this end, an intensive review of documents which articulate its purpose, its structure, and its philosophy will be undertaken. Participant observation will also be employed to gain a better understanding of the issues which have not been formally documented. Second, an attempt will be made, through interviews with a small sample (10%) of the members, to determine who has joined the union and for what reasons. The study will focus on the members' views about the relationship between the values associated with professionalism versus unionism. Finally, the results of the interviews will be used to design a structured questionnaire which will be sent to the entire membership of the union. For comparative purposes a version of the same questionnaire will be sent to a random sample of physicians who have been solicited to join the union but have not done so. The rationale for this research sequence follows from the fact that there is an absence of substantive information to guide a more structured formulation of questions about specific issues. Research concerning this topic is currently of practical as well as theoretical value in view of the increasing likelihood of greater governmental intervention in the practice of medicine through the passage of national health insurance legislation.